流体动力学Hydrodynamics

流体动力学Hydrodynamics(中文4900字,英文3400字)
流体动力学 可压缩气体的流动
可压缩气体的流动速度是可与声音的速度媲美，甚至超越声速的。这种气体的压缩是发生在气体从一个地方移动到另一个地方时发生密度变化引起的，这种变化不可忽视。
假设流体是气体而且在足够低的压力下满足理想状态方程。方程（118）使用，其导热系数是如此的低以至于压缩气体和少量部分的气体可以被视为绝热气体。（见上文）。在这种情况下，它遵循方程（120）描述的那样，密度的变化伴随着许多微妙的压力变化，dp，是这样的：
 
这样通过整合方程的右边使得方程（131）从而得到伯努利方程，成为可压缩气体定律，它是这样描述的：
 
接着简化，一个等价方程：
 
值得一提的是，当气体通过喷嘴或通过叶片前缘时（见下文），这些流体，尽管绝热，在热力学性质中是不可逆的。因此，气体的熵并不一定连续在这种流动中，并因此对方程（120）中的应用是指的商榷的。所幸的是，通过（141）或（140）所表达的结果可以通过讨论被否决而不在方程（131）中涉及。从而判定这是否是稳定有效的绝热流。

Hydrodynamics
Hydrodynamics   Compressible flow in gases
Compressible flow refers to flow at velocities that are comparable to, or exceed, the speed of sound. The compressibility is relevant because at such velocities the variations in density that occur as the fluid moves from place to place cannot be ignored.
Suppose that the fluid is a gas at a low enough pressure for the ideal equation of state, equation (118), to apply and that its thermal conductivity is so poor that the compressions and rarefactions undergone by each element of the gas may be treated as adiabatic (see above). In this case, it follows from equation (120) that the change of density accompanying any small change in pressure, dp, is such that
 
This makes it possible to integrate the right-hand side of equation (131), and one thereby arrives at a version of Bernoulli's law for a steady compressible flow of gases which states that